The invention relates to a cryogenic storage device, in particular for the cryogenic storage of biological samples, and to a method for operating a cryogenic storage device.
It is known in biology, biotechnology, pharmacology and medicine to store samples of biological material in a frozen state. In order to maintain the vitality of the samples over a relatively long period of time, very low temperatures are required for this, for example, the temperature of liquid nitrogen or of liquid nitrogen vapor. A recrystallization in the samples, which could result in the sample material being destroyed, can be avoided for months and years at such low temperatures. Such cryogenic samples are usually stored in cryogenic containers which are usually vacuum-insulated, known as cryogenic tanks. Such cryogenic tanks can be cooled for example by liquid nitrogen which is located in a liquid bath at the bottom of the cryogenic tank. The samples are often stored on shelves, known as racks, which in the gas phase are arranged above the liquid nitrogen. Such a cryogenic tank is disclosed for example in DE 103 32 799 A1. In order to maintain the cooling for a long period of time, usually a refilling with liquid nitrogen is necessary.
During storage of the biological samples, it is important that the samples on the one hand do not come into contact with the cooling fluid and on the other hand are also not unduly heated. Such mistakes can lead to an irretrievable loss of the sample material. In particular, the maintaining of sufficient cooling is very important for the quality of the cryogenic storage. When refilling the cryogenic container with liquid nitrogen, however, an overfilling with liquid nitrogen may occur under some circumstances. In this case, the samples in the racks arranged above the liquid reservoir may come into contact with the liquid nitrogen and may thus be destroyed. In order to avoid any overfilling of the nitrogen reservoir at the bottom of the cryogenic container, therefore, filling level sensors and automatic valve control mechanisms are used. Particularly at the aforementioned low temperatures, however, failure of a filling level sensor or of the fluid valves regulating the supply of nitrogen may occur, which may lead to overfilling.
Another risk to the samples lies in a heating of the samples, which can lead to a recrystallization or in the worst case to a melting of the samples. This may be caused for example as a result of defective insulation of the cryogenic container. Since a loss of samples may occur in the event of such malfunctions, there is a need to protect the samples stored in the cryogenic tank in the event of a malfunction.
It is therefore an objective of the invention to provide an improved cryogenic storage device and an improved method for operating a cryogenic storage device, by means of which the abovementioned problems can be avoided. In particular, it is an objective of the invention to provide a device and a method by means of which it is possible to prevent the samples stored therein or stored in this way from being destroyed or damaged as a result of one of the malfunctions mentioned above.
The object is achieved by a device and a method according to the invention.